[unreadable] As the need in clinical positron emission tomography (PET) has grown in the last few years, there is an increased need for improved lesion detection and for shorter imaging times. The main thrust for this grant application will be the investigation, design, and construction of a 3-D PET scanner based on new Lanthanum scintillators. LaBr3 has faster decay than GSO and LSO and has much better energy resolution than these two scintillators which are currently used in state-of-the-art 3-D PET scanners. 3-D imaging for clinical PET is ultimately limited by randoms and, especially for heavy patients, the combination of scatter and randoms. Thus, even with somewhat lower stopping power than GSO, it is possible to develop a PET scanner with LaBr3 that will achieve much higher performance for clinical whole-body studies due to its superior energy resolution (4% at 511 keV). Further, the combination of very high light output and fast decay opens the possibility of time-of-flight with LaBr3, which will provide an additional gain of a factor of 2 in signal-tonoise ratio translating into significantly better image quality. [unreadable] [unreadable] The significance of this work is that we are moving in a direction of improved PET performance, without driving up the cost of the instrument. Although there is certainly a high cost of developing new technology, the long-term cost of the Lanthanum scintillators is not expected to be high, since the melting point is similar to that of NaI(T1). It is the high melting point of GSO and LSO that makes these scintillators so costly. Therefore, if we are successful in the work proposed in this application, we plan to develop a PET scanner based on LaBr3 that need not be more expensive than current PET scanners, but with markedly superior imaging performance to current state-of-the-art GSO and LSO PET scanners. [unreadable] [unreadable]